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Subject: Re: [PATCH v10 1/8] PCI: Add pcie_reset_flr to follow calling
 convention of other reset methods
To:     Bjorn Helgaas <helgaas@kernel.org>
CC:     Amey Narkhede <ameynarkhede03@gmail.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        <alex.williamson@redhat.com>,
        Raphael Norwitz <raphael.norwitz@nutanix.com>,
        <linux-pci@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kw@linux.com>, Sinan Kaya <okaya@kernel.org>,
        Len Brown <lenb@kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>
References: <20210728202303.GA847802@bjorn-Precision-5520>
From:   Shanker R Donthineni <sdonthineni@nvidia.com>
Message-ID: <64a0049e-00dc-8b10-6c9a-0b270c0a181d@nvidia.com>
Date:   Wed, 28 Jul 2021 16:58:14 -0500
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Hi Bjorn,

On 7/28/21 3:23 PM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Wed, Jul 28, 2021 at 01:54:16PM -0500, Shanker R Donthineni wrote:
>> On 7/27/21 5:12 PM, Bjorn Helgaas wrote:
>>> On Fri, Jul 09, 2021 at 06:08:06PM +0530, Amey Narkhede wrote:
>>>> Add has_pcie_flr bitfield in struct pci_dev to indicate support for PCIe
>>>> FLR to avoid reading PCI_EXP_DEVCAP multiple times.
>>>>
>>>> Currently there is separate function pcie_has_flr() to probe if PCIe FLR
>>>> is supported by the device which does not match the calling convention
>>>> followed by reset methods which use second function argument to decide
>>>> whether to probe or not. Add new function pcie_reset_flr() that follows
>>>> the calling convention of reset methods.
>>>>
>>>> Signed-off-by: Amey Narkhede <ameynarkhede03@gmail.com>
>>>> ---
>>>>  drivers/crypto/cavium/nitrox/nitrox_main.c |  4 +-
>>>>  drivers/pci/pci.c                          | 59 +++++++++++-----------
>>>>  drivers/pci/pcie/aer.c                     | 12 ++---
>>>>  drivers/pci/probe.c                        |  6 ++-
>>>>  drivers/pci/quirks.c                       |  9 ++--
>>>>  include/linux/pci.h                        |  3 +-
>>>>  6 files changed, 45 insertions(+), 48 deletions(-)
>>>>
>>>> diff --git a/drivers/crypto/cavium/nitrox/nitrox_main.c b/drivers/crypto/cavium/nitrox/nitrox_main.c
>>>> index facc8e6bc..15d6c8452 100644
>>>> --- a/drivers/crypto/cavium/nitrox/nitrox_main.c
>>>> +++ b/drivers/crypto/cavium/nitrox/nitrox_main.c
>>>> @@ -306,9 +306,7 @@ static int nitrox_device_flr(struct pci_dev *pdev)
>>>>               return -ENOMEM;
>>>>       }
>>>>
>>>> -     /* check flr support */
>>>> -     if (pcie_has_flr(pdev))
>>>> -             pcie_flr(pdev);
>>>> +     pcie_reset_flr(pdev, 0);
>>> I'm not really a fan of exposing the "probe" argument outside
>>> drivers/pci/.  I think this would be the only occurrence.  Is there a
>>> way to avoid that?
>>>
>>> Can we just make pcie_flr() do the equivalent of pcie_has_flr()
>>> internally?
>>>
>> I like your suggestion don't change the existing definition of
>> pcie_has_flr()/pcie_flr() and define a new function pcie_reset_flr()
>> to fit into the reset framework. This way no need to modify
>> logic/drivers outside of driver/pci/xxx.
>>
>> int pcie_reset_flr(struct pci_dev *dev, int probe)
>> {
>>         if (!pcie_has_flr(dev))
>>                 return -ENOTTY;
>>
>>         if (probe)
>>                 return 0;
>>
>>         return pcie_flr(dev);
>> }
> Can't remember the whole context of this in the series, but I assume
> this would be static?

It should be static since it's referenced in driver/pci/qrirk.c and aer.c.

>> And add a new patch to begging of the series for caching 'devcap' in
>> pci_dev structure.
>>
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -333,6 +333,7 @@ struct pci_dev {
>>         struct rcec_ea  *rcec_ea;       /* RCEC cached endpoint association */
>>         struct pci_dev  *rcec;          /* Associated RCEC device */
>>  #endif
>> +       u32             devcap;         /* Cached PCIe device capabilities */
>>         u8              pcie_cap;       /* PCIe capability offset */
>>         u8              msi_cap;        /* MSI capability offset */
>>         u8              msix_cap;       /* MSI-X capability offset */
>>
>>
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -31,6 +31,7 @@
>>  #include <linux/vmalloc.h>
>>  #include <asm/dma.h>
>>  #include <linux/aer.h>
>> +#include <linux/bitfield.h>
>>  #include "pci.h"
>>
>>  DEFINE_MUTEX(pci_slot_mutex);
>> @@ -4630,13 +4631,10 @@ EXPORT_SYMBOL(pci_wait_for_pending_transaction);
>>   */
>>  bool pcie_has_flr(struct pci_dev *dev)
>>  {
>> -       u32 cap;
>> -
>>         if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
>>                 return false;
>>
>> -       pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
>> -       return cap & PCI_EXP_DEVCAP_FLR;
>> +       return !!FIELD_GET(PCI_EXP_DEVCAP_FLR, dev->devcap);
> Nice, thanks for reminding me of FIELD_GET().  I like how that works
> without having to #define *_SHIFT values.  I personally don't care for
> "!!" and would probably write something like:
>
>   return FIELD_GET(PCI_EXP_DEVCAP_FLR, dev->devcap) == 1;

Both are same since FLR is a single bit value.

>>  }
>>
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -19,6 +19,7 @@
>>  #include <linux/hypervisor.h>
>>  #include <linux/irqdomain.h>
>>  #include <linux/pm_runtime.h>
>> +#include <linux/bitfield.h>
>>  #include "pci.h"
>>
>>  #define CARDBUS_LATENCY_TIMER  176     /* secondary latency timer */
>> @@ -1498,8 +1499,8 @@ void set_pcie_port_type(struct pci_dev *pdev)
>>         pdev->pcie_cap = pos;
>>         pci_read_config_word(pdev, pos + PCI_EXP_FLAGS, &reg16);
>>         pdev->pcie_flags_reg = reg16;
>> -       pci_read_config_word(pdev, pos + PCI_EXP_DEVCAP, &reg16);
>> -       pdev->pcie_mpss = reg16 & PCI_EXP_DEVCAP_PAYLOAD;
>> +       pci_read_config_dword(pdev, pos + PCI_EXP_DEVCAP, &pdev->devcap);
>> +       pdev->pcie_mpss = FIELD_GET(PCI_EXP_DEVCAP_PAYLOAD, pdev->devcap);
>>